A variety of methods have been developed to facilitate the transfer of genetic material into specific cells, e.g., gene therapy. These methods are useful for both in vivo or ex vivo gene transfer. In the former, a gene is directly introduced (intravenously, intraperitoneally, aerosol, etc.) into a subject. In ex vivo (or in vitro) gene transfer, the gene is introduced into cells after removal of the cells from specific tissue of an individual. The transfected cells are then introduced back into the subject.
Delivery systems for achieving in vivo and ex vivo gene therapy include viral vectors, such as a retroviral vector or adenovirus vectors, microinjection, electroporation, protoplast fusion, calcium phosphate, and liposomes (Felgner, et al., 1987; Mulligan, 1993; Morishita, et al., 1993).
Liposomal mediated gene therapy has, for example, involved the use of cationic liposomes formed from LIPOFECTIN , a reagent consisting of a cationic lipid and a neutral lipid (Felgner, et al., 1989, 1993). Other liposomal-mediated methods of gene therapy have been described (Trubetskoy, et al., 1992; Morishita, et al., 1993; Rose, 1994), where electrostatic complexes of cationic liposomes and DNA are formed. More recent approaches to liposome-based transfection compositions have included a polycation, such as protamine or polylysine, to bind the DNA to the lipid particles (Wagner, et al., 1991) or to condense the DNA (Gao and Huang, 1996; Li and Huang, 1996).
However, the liposomal-mediated gene therapy methods and compositions described to date have recognized limitations, including, for example, the toxicity of LIPOFECTIN, the large size of the DNA-liposome complexes, and rather poor in vivo transfection efficiencies.
It would be desirable, therefore, to produce a DNA plasmid-liposome complex which is relatively non-toxic, is sized for intravenous administration, and has a high transfection efficiency.